The summer solstice is here once again, marking this the longest 24-hour daylight period of the year and the start of astronomical summer in the U.S.
At 1:04 a.m. EDT, the sun was straight overhead along the Tropic of Cancer, while the North Pole reached its maximum annual tilt toward the sun.
As our amazing planet rotates on its axis, areas within the Arctic Circle see the sun circle through the sky for 24 hours. But that's only a select few.
Still, most places in the U.S. see the sun for 14-16 hours on the summer solstice, depending on latitude, with an elongated dawn and dusk as well.
What makes this day so interesting, or significant in astronomical terms? A lot of things, actually. Here are some Summer Solstice 2013 fun facts:
1. North of the Tropic of Cancer, the sun takes its longest and highest path through the sky. The higher your latitude, the longer your day will be.
This also means the sun will appear lower in the sky. In more northern locations, the sun is up longer, but shines from a lower angle at mid-day.
2. The sun rises and sets at its northernmost points on the horizon, relative to due east and due west, respectively, that you will see at any point.
This is true even in the Southern Hemisphere, where the script is flipped - the June solstice is the shortest day of the year, and December's the longest.
3. The farther one goes from the equator, the closer sunrise and sunset appear to due north on a compass, practically overlapping at the Arctic Circle.
4. The summer solstice has one of the earliest sunrises of the year (but not necessarily the earliest). Your earliest sunrise was likely a day or two ago.
Even though the June solstice marks the longest day of the year in the Northern Hemisphere overall, the earliest sunrise takes place a little before.
The cause of this barely-noticeable misalignment is a discrepancy between our clocks and the apparent motion of the sun with respect to the horizon.
5. In addition to the day itself being as long as it'll get, the twilight in the Northern Hemisphere is longer on the solstice than at other time of year.
The fact that the summer solstice features the shortest night of the year also means that the sun doesn’t drop as far below the horizon at night.
Therefore, the sun’s path tends to curve slowly below the horizon instead of plummeting, resulting in longer periods of twilight in morning and at night.
While the longer period of twilight is less discernible at lower latitudes, northern cities experience noticeably longer dawn and dusk on the solstice.
So there you go. Enjoy it!